The Correction of Myopic Evaluation Trial (COMET) is a multi-center, randomized, double-masked clinical trial that aims to assess whether progressive addition lenses (PAL's) slow the progression of juvenile- onset myopia, as compared to conventional single vision lenses (SV). The primary outcome measure is progression of myopia, as measured by cycloplegic autorefraction. An additional outcome measure is axial elongation, as measured by A-scan ultrasonography. The secondary aim of COMET is to describe the natural history of juvenile-onset myopia in a group of children receiving conventional treatment or PAL's. Within a one-year period, the study will enroll 450 children, 6-12 years old, with myopia (-1.25D to -4.5D) in both eyes, who meet specific inclusion and exclusion criteria. Participants will be identified primarily from elementary school vision screening and College of Optometry clinics. Eligible children will be examined according to a standard protocol at baseline and six-month intervals, for at least three years, to measure changes in refractive error and to update prescriptions. The proposed COMET is a collaborative effort that involves four clinical centers at Colleges of Optometry in Boston, Birmingham, Philadelphia and Houston, a study chair's office in Boston, Massachusetts and a coordinating center (CC) in Stony Brook, New York. An independent Data Safety and Monitoring Committee will review the data at least once a year to assess the risks and benefits of the lens assignment. This application seeks support for the activities of the CC. The major CC responsibilities are to: 1) provide epidemiologic and biostatistical expertise to the organization, design, conduct and analysis of the trial; 2) collaborate in the development and distribution of forms, documents and protocols; 3) develop, implement and monitor the randomization process; 4) be responsible for data management, processing and analysis; 5) prepare reports to monitor recruitment, data collection, safety issues, endpoints and data quality; 6) coordinate and document study meetings and communications among centers; 7) be responsible for quality assurance procedures; and 8) collaborate in preparing publications of the results.